Stable lead alkyl compositions and a method for preparing the same



Patented Nov. 24, 1953 STABLE LEAD ALKYL COMPOSITIONS AND A METHOD FORPREPARING THE SAME George Calingaert, Geneva, N. Y., assignor to EthylCorporation, New York, N. Y., a corporation of New York No Drawing.Application March 18, 1952, Serial No. 277,282

7 Claims. 1

This invention relates to alkyllead compositions which are stable attemperatures above 100 C. It also relates to methods for inhibiting thethermal decomposition of alkyllead compounds when subjected totemperatures above 100 C., at which temperature thermal decompositionbecomes appreciable.

Generally my invention contemplates inhibiting the thermal decompositionof alkyllead compounds in which at least one valence of the lead issatisfied by an alkyl radical.

More specifically, my invention is concerned with an improved processfor separating alkyllead compounds from the reaction productsaccompanying their synthesis. It is also applicable to a method forinhibiting thermal decomposition of an alkyllead product during itsformation or during any step of the process including blending withother products in making the commercial antiknock fluid. It is applicable to minimizing the possibility of thermal decomposition duringstorage or transportation of an alkyllead product. It is especiallyapplicable to preventing thermal decomposition of mixtures containing ahigh concentration of an alkyllead compound. The likelihood of thermaldecomposition is more of a problem at high concentrations of leadalkyls, i. e., compositions above 80% by weight.

As is well known, tetraalkyllead antiknock compounds generally areproduced by reacting an alloy of lead and a dissimilar metal usuallysodium, with an alkylating agent such as alkyl halide, usually an alkylchloride The tetraalkyllead compound is produced thereby in admixturewith various reaction by-products from which it must be separated.Separation is accomplished ordinarily by steam or vacuum distillationwith subsequent purification of the tetraalkyllead distillate. Due tothe toxic and unstable nature of tetraalkyllead antiknock compounds theforegoing process is subject to many difficulties.

In the manufacturing operations of alkyllead compounds meticuloustemperature control and exact safety measures are of paramountimportance. The rate of decomposition of the al kyllead compoundincreases rapidly with small rises in temperature above the temperaturewhere thermal decomposition becomes appreciable. For example,decomposition of tetraethyllead occurs at the rate of approximately 2per cent per hour at a temperature of 100 C., which is the customarytemperature used in separatingtetraethyllead from the reaction productsaccompanying its synthesis. At tem- (Cl. 26il-437) 2 peratures above C.the decomposition rate increases logarithmically so that a point is soonreached where external heat is no longer required and decompositionbecomes self-propagating.

Generally the manufacture of a tetraalkyllead, for example,tetraethyllead, involves the following steps: reaction, separation fromreaction products, purification and blending. The reaction andseparation steps of the alkyllead process which are conducted at or neardecomposition temperatures require extensive and careful. precautionarymeasures in order to minimize, and to provide for, excessivedecomposition due to sudden and unavoidable increases in temperature.

Such likelihood of excessive decomposition is present also duringblending, handling, storage and transportation. Prior to diluting thealkyllead concentrate with scavengers, gasoline or other materials, thealkyllead compound remains a concentrate and the problem of excessivethermal decomposition exists, even though the temperature is maintainednormally well below that of decomposition. For example, in thepurification step wherein the tetraethyllead concentrate is washed andblown with air at atmospheric temperature to remove impurities, a suddenincrease in temperature may occur due to the oxidation oftriethylbismuth which is present as an impurity. Also pumps used inhandling tetraethyllead occasionally freeze and the friction developedmay cause a local overheating to a temperature above the temperature ofdecomposition of the tetraethyl lead. Faulty wiring, leaks onto steampipes, and other accidental causes also may produce local overheatingwith result ng dangerous decomposition.

Therefore, it is an object of my invention to stabilize alkylleadcompounds in which at least one valence of the lead is satisfied by analkyl radical, against thermal decomposition during one or more of thefollowing operations: manufacture, purification, blending,transportation and storage.

I accomplish this object by incorporating with alkyllead compounds arelatively small quantity of a material which I have found has theproperty of inhibiting and substantially preventing their decompositionwhen subjected to elevated temperature conditions. Furthermore, Iaccomplish this object by conducting one or more steps of themanufacturing process for the alkyllead compound. particularly theseparation 3 step, in the presence of such a material. The materialswhich I have found to possess this property are referred to hereinafteras thermal stabilizers.

These thermal stabilizers ar various difierent types of compounds.Fused-ring hydrocarbons and halogenated derivatives of thesehydrocarbons are particularly effective, as well as unsaturatedcompounds having boiling points at least as high as 1 C. at atmosphericpressure. Of these unsaturated compounds best results are obtained whenthey are olefin hydrocarbons in= eluding aryl-substituted olefins. Thesubstitution of halogens for part or all of the hydrogen atoms in suchunsaturated compounds also gives highly effective thermal stabilizers.

Aliphatic nitro compounds, as well as aliphatic nitrates and aliphaticnitrites, form another very effective class of thermal stabilizersaccording to the present invention.

Compounds that have a boiling point below 1 C. at atmospheric pressureare of no appreciable value as thermal stabilizers. It appears that suchcompounds in addition to their low effectiveness are substantiallyinsoluble in the alkyllead compounds to be stabilized, and canaccordingly not be mixed with these compounds in the desiredproportions.

I have found that my thermal stabilizers when used in amounts varyingfrom 0.01 to 5.0 per cent by weight of the lead alkyl product areeffective in substantially retarding or preventing thermal decompositionat temperatures above 100 C. for an extended period of time, c. g., tento twenty hours at 130 C., which period is sufilcient for allcontemplated commercial applications.

A representative group of my thermal stabilizers are the following:crotonaldehyde, allo-- ocimene, butadiene, di-amylene, dipentene,heptene, trimethylethylene, styrene, divinyl-benzene, cyclohexene,dicyclopentadiene, allyl iodide, chloroprene, hexachloropropylene,ethynylcyclohexanol, glyceryl monos'te'arate, glycol dilau-rate', tiglicalcohol, alloxan, azobenzene, 2,2'--azonaph thalene,4benzeneazo-l-naphthylamine, n-butyl nitrate, n-butyl nitrite,triphenylchlormetliane, nitroethane, nitromethane, 2-nitro*2-methyl-1-'propanol, p-nitro benzoic acid, p-nitroaniline, allyl isothiocyanate,anthracene, chryse'ne', naph thal-ene, alpha-methyl naphthalene,bromonaphthalene, chloronaphthalene, alphanaphthol, beta-naphthol,naphthoresorcinol, beta-naphthoquinoline, tetrahydronaphthalene,in'dene, stearyl iodide, styrene dibromide, phloroglucinol,di-isobutylene, tetramethylethylene, tribromoethylene, oleic acid,cinnamic acid dibromide, maleic anhydride, phthalic' anhydride, aluminumoleate, ethyl thioc'yanate, hexachloroethane,Z-amino-Z-methyl-l-propanol',. 2'-ethyl= 1,3-hexanediol, iodoform,furfural, chlorophyll, lecithin, pyrophosphaditic acid, sem-i-carbazidehydrochloride, stilbene, methyl styrene, o-bromo styrene,p-chlorostyrene, o-ethylstyrene, o-' chlorostyrene. aconitic acid,ethylene dibromide, resorcinol, 2,4,6-tri(dimethylaminomethyl)phenol,2-methyl-2, l-pentanediol, ethylene bromo= hydrin, alpha-terpineol,acetyl aminothiophene, ethanolamine, p,p'-diaminodiphenylmethane,acridine, furfuryl alcohol, fu'rfu'ryl amine, S-hydroxyquinaldine,lepidine. Of these compounds the butadiene has the lowest boiling point,its

boilin point being about 1 C. at atmospheric pressure.

. To illustrate the efiectiveness of the present invention, directcomparisons were made between alphathe decomposition rates ofunstabilized and stabilized tetraethyllead. A thermostaticallycontrolled hot oil bath was fitted with a stirrer, thermometer, and aholder for a small reaction tube. A c. c. gas buret beside the bath, andequipped with a water-containing levelling bottle, was connected bymeans of rubber tubing with the reaction tube after the desired samplewas introduced into this tube. After the bath was brought to a steadytemperature of 160 C., the sample-containing tube was quickly introducedand clamped with the levelling bottle adjusted to hold the gas buret inplace at a zero reading. As the sample decomposed under the influence ofthe bath temperature, readings were taken over various periods of theamount of gases thus liberated, as indicated by the gas buret.

With pure tetraethyllead used in one milliliter amounts, 10 c. c. of gaswas liberated in one minute, and 100 c. c. of gas in about six minutes.However, if to the" same amount of tetraethyllead there is previouslyadded 2% by weight of furfura'l or 2-ethyl-l,3-hexanediol, at the end of100 minutes only four 0. c. of liberated gas was shown. When 2%ethynyl-cyclohexinol is used instead of the other stabilizers, even lessgas is liberated. The other stabilizers listed above showed about thesame degree of eiiectiveness.

The liberation of gas is a very good index of the alkyl-leaddecomposition. The principal decomposition products are metallic leadand hydrocarbon gas. When the decomposition becomes self-propagating,the rate or gas liberation changes from a gradual one to one thatbecomes very rapid. With the above stabilizers tested at 160 C., therewas no serious rise in gas liberation rate. Normally, however, thedecomposition of unstabilized tetraethyllead will become uncontrollableif it is heated to C., whether this temperature isreached rapidly orslowly, unless it is possible to very rapidly cool it down to about 100C. or below.

The above described behavior of the listed stabilizers also takes placewith other alkyllead compounds such as triethyllead bromid andtetrapropyl lead. In fact these compounds when stabilized can be boiledand distilled at atmospheric pressure, something never before possiblebecause they uncontrollably decompose before they can be heated to thesetemperatures.

My invention is adapted to the stabilization of tetraethyllead and otheralkyllead compounds at various stages during synthesis, separation,purification and blending with other materials. For example one of mythermal stabilizers may be added to the reactants from which thealkyllead compound is produced, regardless of the particular reactionemployed. Preferably it is added prior to the separation step which isconducted at a temperature close to the temperature where hazardousrun-away decomposition is particularly prevalent. By adding one of mythermal stabilizers to the reaction mixture prior to distillation, thedanger arising from unexpected temperature increases is substantiallyeliminated. Also-my thermal stabilizers may be employed to stabilize thealkyllead compound both in storage and in shipping and especially tostabilize any alkyllead concentrate. If elevated temperature conditionsare likely to be encountered, the addi tion of a small amount of thermalstabilizer to the alkyllead compound will economically andsatisfactorily eliminate most of the hazard involved. While meticuloustemperature control and exacting safety measures have been successful inreducing to a minimum the hazards of processing and handling oftetraethyllead, the use of my invention provides a factor of safety farbeyond that presently enjoyed. Furthermore, waste of the alkylleadproduct due to decomposition is considerably minimized through the useof my invention.

My invention is useful in stabilizing alkyllead compounds in which atleast one valence of the lead is satisfied by an alkyl radical. Forexample tetraethyllead, tetramethyllead, tetrapropyllead,dimethyldiethyllead, triethylphenyllead and triethyllead bromide can besuccessfully stabilized against thermal decomposition by incorporatingtherein a relatively small quantity of one of my stabilizers.

Depending upon the conditions to which said alkyllead compound issubjected or likely to be subjected, the stabilizer can be selected tobe stable to oxidation and/ or to be nonpolymerizable at the temperatureof reaction of the alkyllead compound. It should be non-objectionable ascontained in the final product, and if it is desired to distill thestabilized material, the stabilizer should have a vapor pressure withinthe range of the alkyllead product. Besides relative effectiveness,generally all the above properties should be taken into account inselecting the best commercial stabilizer for a given alkyllead compound.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope hereof, it is to beunderstood that the invention is not limited to the specific embodimentshereof, except as defined in the appended claims.

This application is a continuation-in-part of my co-pending application,Serial Number 64,259, filed December 8, 1948.

What is claimed is:

1. A method of inhibiting the decomposition of an alkyllead compoundcomprising incorporating therewith a thermal stabilizer selected fromthe class consisting of glyceryl monostearate, glycol dilaurate, 2methyl 2,4 pentanediol, ethylene bromohydrin, furfuryl alcohol,ethynylcyclohexanol, tiglic alcohol, a-terpineol, crotonaldehyde,Z-amino-Z-methyl-l-propanol, 2-ethyl-1,3- hexanediol and furfural.

2. A method of inhibiting the decomposition of a tetraethyllead,concentrate comprising incorporating therewith from 0.01 to 5.0 per centby Weight of a thermal stabilizer selected from the class consisting ofglyceryl monostearate, glycol dilaurate, 2 methyl 2,4 pentanediol,ethylene bromohydrin, furfuryl alcohol, hexanol, tiglic alcohol,a-terpineol, crotonaldeethynylcyclohyde, 2-amino-2-methyl-1-propanol,2-ethy1-1,3- hexanediol and furfural.

3. In a process of producing tetraethyllead by reacting a sodium-leadalloy with ethyl chloride and separating the thus producedtetraethyllead from the reaction mass by steam distillation, the stepwhich comprises conducting said steam distillation in the presence of athermal stabilizer selected from the class consisting of glycerylmonostearate, glycol dilaurate, 2-methyl-2,4- pentanediol, ethylenebromohydrin, furfuryl alcohol, ethynylcyclohexanol, tiglic alcohol,aterpineol, crotonaldehyde, 2-amino-2-methyl-1- propanol,2ethy1-1,3-hexanediol and furfural.

4. A new composition comprising an alkyllead compound and a thermalstabilizer selected from the class consisting of glyceryl monostearate,glycol dilaurate, 2-methyl-2,4-pentanediol, ethylene bromohydrin,furfuryl alcohol, ethynylcyclohexanol, tiglic alcohol, terpineol,crotonaldehyde, 2-amino-2-methyl-1-propanol, 2ethyl-1,3- hexanediol andfurfural.

5. A new composition comprising at least eighty per cent by weight oftetraethyllead and less than five per cent of an organic thermalstabilizer selected from the class consisting of glyceryl monostearate,glycol dilaurate, 2-methyl-2,4-pentanediol, ethylene bromohydrin,furfuryl alcohol, ethynylcyclohexanol, tiglic alcohol, a-terpineol,crotonaldehyde, 2-amino-2-methyl-l-propanol, 2-ethyl-1,3-hexanediol andfurfural.

6. The process which comprises distilling an alkyllead compound atatmospheric pressure from a mixture containing said alkyllead compoundand a stabilizer selected from the class consisting of glycerylmonostearate, glycol dilaurate, 2- methyl-2A-pentanediol, ethylenebromohydrin, furfuryl alcohol, ethynylcyclohexanol, tiglic alcohol,a-terpineol, crotonaldehyde, 2-amino-2- methyl-I-propanol,2-ethyl-1,3-hexanediol and furfural.

7. In a process for steam distilling an alkyllead compound, the step ofincorporating with said compound, before steam distillation, a thermalstabilizer selected from the class consisting of glyceryl monostearate,glycol dilaurate, 2-methyl- 2,4-pentanediol, ethylene bromohydrin,furfuryl alcohol, ethynylcyclohexanol, tiglic alcohol, aterpineol,crotonaldehyde, 2-amino-2-methyl-lpropanol, 2-ethyl-1,3-hexanediol andfurfuryl.

GEORGE CALINGAERT.

Name Date Linch Dec. 9, 1947 Number

1. A METHOD OF INHIBITING THE DECOMPOSITION OF AN ALKYLLEAD COMPOUNDCOMPRISING INCORPORATING THEREWITH A THERMAL STABILIZER SELECTED FROMTHE CLASS CONSISTING OF GLYCERYL MONOSTERATE, GLYCOL DILAURATE, 2 -METHYL - 2,4 - PENTANEDIOL, ETHYLENE BROMOHYDRIN, FURFURYL ALCOHOL,ETHYNYLCYCLOHEXANOL, TIGLIC ALCOHOL, A-TERPINEOL, CROTONALDEHEXANEDIOLAND FURFURAL.